Vulcanization of rubber



Patented Oct. 28, 1941 Ira Williams, Woodstown, N. J., assignor to E. I. Du Pont de Nemours & Company, Wilmington, I Del., a corporationof Delaware No Drawing. Application Novemberol8, 1938,,

. Serial No. 241,139

18 Claims. (c1. 260-7883 This invention relates to the vulcanization of rubber and more particularly to a new class of substances which are accelerators of vulcanization.

The vulcanization of rubber is old in the art and'many classes of substances have been employed as vulcanization accelerators. Among the more common materials which have been employed are salts and esters of disubstituted di' thio-carbamic acids, substituted guanidines, substituted thioureas, aldehyde amine condensation products and mercapto-arylene-thiazoles. Each of these classes of accelerators produce slightly different results and each has found application under conditions to which it is best suited.

It is an object of the present invention to provide a new class of accelerators for the vulcanization of rubber. A further object is to provide a new class of accelerators, the use of which will avoid premature vulcanization during the processing of the rubber and which accelerators are of utility under new and different conditions A still further object is to provide a method for vulcanizing rubber.

Still other objects are to produce new compositions of matter and to advance the art.

The above objects may be accomplished by adding to a rubber mix, prior to vulcanization, a small amount of a 2-amino-thiazoline compound. By a 2-amin0-thiazoline compound, I wish to include Z-amino-thiazoline which has the formula H2C--N /(2JNHz H2C'S 5 1 derivatives thereof in which one or more of the hydrogens are replaced by one or more alkyl or aryl groups and weak acid salts of such thiazolines. .I have found that these amino-thiazolines are, as a class, very effective accelerators for the vulcanization of rubber, having many of the vulcanization characteristics of the mercaptoarylene-thiazoles, but having the advantage that they are substantially inactive at a temperature of 227 F. and below.

The preferred class of amino-thiazolines of my in which X represents hydrogen or an alkyl radical and R. represents-hydrogen or an. alkyl or aryl radical. When thecompounds contain aryl radicals, such aryl radicalsv may contain clude radicals of the, benzene, naphthalene, phenanthrene, diphenyl and like series, but will preferably be of the benzene or'naphthalene series. Preferably the alkyl radicals will be the lower alkyl radicals, that is, those containing from ,1 to 6 carbonatoms, but may be long-chain-alkyl radicals. While the thiazolines of my invention maycontain aryl groups-the most effective compounds appear to be those in which. the substituents, when present, consist'of alkyl radicals.

The Z-amino-thiazolines-of my invention are basic compounds which readily form salts with acids. Their salts with strong acidsghave not proved; to be satisfactory as accelerators.- However, salts formed from weak acids, that is, acids not stronger than formic acid (Ka 1O =abou 2), are satisfactory accelerators.

In order to illustrate my invention more clearly, the preferred modesof carrying the same into effect and the advantageous results to be obtained thereby, the following examples are given:

. E:1:ample 1 1 A mixturefof .100 parts of rubber, 5 parts of zinc oxide, 25 parts-of carbon black, 3 parts of sulfur and'3 parts of stear'ic acid was prepared and portions were treated with 1 part of. various Z-amino-thiazolines. The compounds werethen cured at 287 F.' and tested with the following results:

1 Y gfii -gggzg Tensile strength Thiazoline I 20 min." mini 20 me. 60 min.

2phenylamino-thiaz'olihe. 975 I 2050 2050 3600 2-methylamino-thiazoline 1450 t 2750 .3250 3850 2-amino-5-methyl-thiazoline 1075 2175 2375 3675 2-a min0-5:5-dimethyl-thiazol1ne -4- 1000 2125 2350 3650 2= ethylamm0-5-methyl-t a- I zoline. 1125 2375 2525 4100 -Z-butylannno-5-methyl-thia- Y zol1ne 900 2250 2225 4100 2-diethylammo-5-methyl-thi- I azolme 750 1700 1650 2875 'None of the above compounds vulcanized in 30 ,-.minutes at 227F.

the spirit of my invention.

Example 2 The rubber mixture used in Example 1 was treated with one part of various salts of Z-amino- 5-methyl-thiazoline and the vulcanization characteristics of the compound were determined.

Accelerator Vulcanization characteristics Dicthyl-dithio carbamic acid sa1t.

2-mercapto-benzothiazole salt Acetate Hydrochloride A very active accelerator at Active at 260 F.

N practical value.

Other compounds falling within my invention and which I have found to be accelerators for the vulcanization of rubber are the following:

While the examples illustrate the use of these products under one set of conditions, they are valuable under a wide variety of conditions. The rubber composition may be altered to contain any of the compounding ingredients available for use in rubber and the amount of sulfur may be varied to produce the desired results. The amount of the amino-thiazoline 'may also be varied considerably but the amount to be preferred lies between about 0.1% and about 5% of the weight of the rubber. The temperature of vulcanization may also be altered to suit the particular conditions.

The amino thiazolines constitute a class of accelerators which produce no discoloration in the rubber and which are particularly free from activity at processing temperatures. In contrast to the thioureas, dithio-carbamates and mercapto-arylene thiazoles, they may be used in the presence of basic substances such as the guanidines without causing premature vulcanization.

Also, my compounds may be employed with other accelerators such as the acidic type sulfurcontaining accelerators to activate the same in the same manner as and in place of the guanidines.

While I have disclosed the preferred embodiments of my invention and the preferred modes of carrying the same into effect, it will be readily apparent to those skilled in the art that many variations and modifications can be made in the compounds employed and in the conditions under which they are employed without departing from Accordingly the scope of my invention is to be limited solely by the appended claims construed as broadly as is permissible in view of the prior art.

I claim:

1. The method of vulcanizing rubber which comprises incorporating into the rubber mix,

thiazolprior to vulcanization, a small amount of a 2-amino-thiazoline compound of the group con- Weak acids.

Moderately active at 287 I prior to vulcanization, a small amount of a 2-amino-thiazoline which, except for the nitrogen of the amino group and the nitrogen and sulfur of the thiazoline ring, consists of carbon and hydrogen and is free of aromatic rings.

3. The method of vulcanizing rubber which comprises incorporating into the rubber mix, prior to vulcanization, a small amount of a weak acid salt of a 2-amino-thiazoline which, except for th nitrogen of the amino group and the nitrogen and sulfur of the thiazoline ring, consists of carbon and hydrogen and is free of aromatic rings.

'2. The method of vulcanizing rubber which comprises incorporating into the rubber mix,

4. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a 2-amino-thiazoline compound of the group consisting of 2-amino-thiazolines and their salts of weak acids.

5. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a 2-amino-thiazoline.

6. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a 2-amino-thiazoline which, except for the nitrogen of the amino group and the nitrogen and sulfur of the thiazoline ring, consists of carbon and hydrogen.

'7. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a Weak acid salt of a 2-amino-thiozoline.

8. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a weak acid salt of a 2-arnino-thiazoline which, except for the nitrogen of the amino group and the nitrogen and sulfur of the thiazoline ring, consists of carbon and hydrogen.

9. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of Z-amino-thiazoline containing at least one alkyl substituent but no other substituents.

10. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of 2-amino-thiazoline containing at least one alkyl substituent on the thiazoline ring and being otherwise free of substituents.

11. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of 2-amino-thiazoline containing at least one methyl substituent on the thiazoline ring and being otherwise free of substituents.

12. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of 2- amino-5-alkyl-thiazoline.

13. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of 2-amino-5 methyl-thiazoline.

14. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of 2-amino-5 S-dimethyl thiazoline.

15. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a weak acid salt of Z-amino-thiazoline containing at least one alkyl substituent on the thiazoline ring and being otherwise free of substituents.

16. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a weak acid salt of 2-amino-5-alkyl-thiazoline.

17. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of a weak acid salt of 2-amino-5-methyl thiazoline.

18. Rubber having incorporated therein, as a vulcanization accelerator, a small amount of the Z-mercapto-benzothiazole salt of 2-amino-5- methyl-thiazoline.

IRA WILLIAMS. 

